Electronic control circuit for controlling the rate of fire of a machinegun



June 24, 1969 K. GRUNDBERG 3,451,307

' ELECTRONIC CONTROL CIRCUIT FOR CONTROLLING THE RATE OF FIRE OF A MACHINEGUN Filed Dec. 6, 1967 o KENNETH GRUNDBERG ATTORNEYS United States Patent Oflice 3,451,307 Patented June 24, 1969 US. Cl. 89-135 Claims ABSTRACT OF THE DISCLOSURE An electronic control circuit for and method of controlling the rate of fire of a machinegun or the like, including means for and the method of selectively providing a full firing rate, a reduced firing rate, one shot at a time, a burst of shots and a selected number of single shots or a slow burst. The control circuit is essentially an output solenoid energized from a source of electrical energy in accordance with the closing of an electronic switch and a multivibrator for selectively closing the electronic switch at controlled intervals; i.e., by means of pulses of electric energy, or for a predetermined time or both.

Means for and a method of absorbing electrical energy from the solenoid on opening of the electronic switch and for protecting the control circuit in case of short circuiting of the solenoid are also disclosed. Provision is also made for extending the initial actuating pulse from the multivibrator to the electronic switch on an initial multivibrator cycle and therefore compensating for lubricating and mechanical rebound of a gun controlled by the control circuit and also for varying the operating parameters of the multivibrator in accordance with the magnitude of the energy source to provide a substantially uniform mechanical operation of the solenoid over a wide range of energy source magnitudes.

BACKGROUND OF THE INVENTION Field of the invention The invention relates to a means for and method of control of a mechanical structure and refers more specifically to a control circuit for controlling the rate of fire of a machinegun or the like and the method of controlling the rate of fire in accordance with the control circuit.

Description of the prior art In the past, machineguns and the like have generally been fired or not fired at the single designed rate of fire thereof. Thus, in many instances ammunition has been fired uselessly. In addition, partly due to the rate of firing in the past, machinegun fire has not been as accurate as desired particularly where the firing rate has not been at the natural frequency of the gun support.

Where conservation of ammunition has been necessary in the past, it has been accomplished by individual gunners controlling the pressing of a machinegun trigger to fire the guns in short bursts or possibly in individual shots. In addition, some mechanical methods of controlling the actual rate of fire of a machinegun have been attempted without particular success in the past.

SUMMARY OF THE INVENTION In accordance with the invention, an electronic control circuit for and method of controlling the rate of firing of a machinegun or the like is provided. The electronic control circuit includes selector switch means for permitting continuous full rate firing of the machinegun, reduced rate firing of the machinegun, firing of one shot at a time, firing of a burst of shots at one time, and for firing a slow burst of shots.

In addition, the electronic control circuit of the invention includes means for absorbing and rapidly dissipating the stored energy in an actuating solenoid connected thereto to assure rapid response of the solenoid and to prevent damage to the electronic control circuit, short circuit protection for the electronic control circuit and structure for compensating the control circuit to provide constant operation of an actuating solenoid connected thereto over a relatively wide range of sources of actuating electrical energy. Means are also included in the control cirsuit for providing compensation during initial firing for operating parameters, such as lubrication and inertia, of a gun controlled thereby and to adjust the firing rate of the gun to the natural frequency of the support therefor to improve the accuracy of the gun.

BRIEF DESCRIPTION OF THE DRAWING The figure is a schematic diagram of an electronic control circuit constructed in accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The electronic control circuit 10 of the invention includes a source of electrical energy 12, a solenoid output coil 14 and the electronic switch 16 positioned therebetween. The coil 14 is energized from the source of electrical energy 12 on closing of the electronic switch 16.

The control circuit 10 further includes the relay circuit 18, including the driver transistor 20 and short circuit protection transistor 22, the butter circuit 24, including the buffer transistor 26, the multivibrator circuit 28 including the transistors 30 and 32, and the transistor 34, the cutoli circuit 36 including the transistors 38 and 40 for stopping the multivibrator 28, the switching circuit 42 and trigger switch 44. The electronic control circuit 10 further includes the energy absorbing circuit 46 including the transistor 48, connected as shown in the figure.

In more detail, the switching transistor 49 of electronic switch 16 is turned on any time the transistor 20* of the relay circuit 18 is energized due to current flowing through resistors 50 and 52 of the switch 16. The transistor 20 is turned on at different times in accordance with the setting of the switching circuit 42. Thus, the coil 14 is energized continuously or intermittently at selected rates to provide dilTerent firing rates for a machinegun actuated on energizing the coil 14 in accordance with the setting of the switching circuit 42.

With the switching circuit 42, as shown in the figure,

in the first position and with the battery 12 connected to the control circuit 10 to provide a voltage of approximately six volts across the Zener diode 56 of the voltage divider formed by the resistor 54 and Zener diode 56, a voltage of approximately six and one-half volts is provided across the resistor 58 in the voltage divider network, including the resistors 60 and 62 through the switching circuit 42 in the first position when the trigger switch 44 is closed. The other half volt between the resistor 62 and the top of the Zener diode 56 is dropped across the diode 64. The voltage at the resistor 58 will cause the capacitor 66 to draw current through the resistors 68 and 70, whereby the transistor 20 will be turned on.

The electronic switch 16 will be turned on when the transistor 20 is turned on, as previously indicated, whereby current will be drawn through the resistors 72 and 74 to place the base of the transistor 22 at a potential to provide a bias on the transistor 22 to maintain the transistor 22 in an on condition bypassing the capacitor 66. Thus, the transistor 20 and therefore the transistor 49 will remain turned on to continuously energize the sole- 3 noid' output'coil' 14 with the switching circuit 42 in the first position and the trigger switch 44 closed. In the case of a machinegun connected to the solenoid output coil 14 'afull rate of fire would thus be produced of, for example 1000 rounds per minute.

In this connection it will be noted that if the solenoid output coil 14 is shorted to ground, that no current will be drawn through the resistors 72 and 74 so that the transister 22 will notbe biased on after the capacitor 66 has been charged so that the transistor 20 would be turned 01f. Short circuit protection for the control circuit 10 is thus provided since the transistor 49 will not be maintained in a conducting condition if the coil 14 is short circuited';

When the switch 16 is opened the voltage at the emitter of the transistor 49 substantially immediately goes from the'value of the positive source of electrical energy 12 to zero volt. This decline in voltage can occur in, for

example, five microseconds. A substantial negative potential then appears at the collector of the transistor 49 due to the decaying voltage in the solenoid output coil 14. It is desired to absorb this negative voltage from the output coil 14 to prevent it from damaging the transistor 49.

To absorb the current from the coil 14 on opening of the switch 16, the transistor 48 of the energy absorbing circuit 46 conducts through the diode 76 when the voltage of the diode 76 is slightly negative. When the transistor 48 conducts, a voltage which is regulated by the Zener diode 78 is built up on the capacitor 80 and across resistor 82. The negative voltage due to the decaying f the energy stored in the output solenoid coil 14 is thus allowed to build to a level allowed by the voltage established by the Zener diode 78 over a period of, for example, one hundred microseconds and remains at this level which the transistor 49 can withstand without damage while still allowing the stored energy in the inductance of the solenoid to dissipate quickly until the energy in the coil 14 has been dissipated at which time the transistor 48 ceases to conduct.

The mechanical actuator 15 is provided in conjunction with the coil 14 to effect the physical firing of, for example, a machinegun controlled by the control circuit 10. The mechanical time of response of the actuator varies inversely with voltage across the coil 14 and is more rapid at higher values of supply voltage. Also, the amount of energy stored in the inductance of coil 14 is proportional to the current flowing in the coil or if the resistance remains constant, proportional to the voltage. Circuit 46 causes the stored energy of coil 14 to discharge at a fixed voltage, the release time of the actuator 15 is thus proportional to the supply voltage. The response of the actuator 15 is thus compensated to maintain the sum of the actuating and release timesrelatively constant over the operating voltage range of the control circuit 10.

With the switching circuit 42 in the second position thereof, illustrated in the figure, and with the source of electrical energy 12 connected to the control circuit 10, the initial voltage on the right side of capacitor 84 will be approximately the six volts across the Zener diode 56.

Before the trigger switch 44 is closed the voltage on the 'left side of the capacitor 84 is substantially zero volt since the left side of capacitor 84 is grounded through resistors 86 and 88, the switching circuit 42 and the resistor 90.

Also, at this time the charge on the left hand side of the capacitor 92 will be zero volt since the left hand side of the capacitor 92 is also grounded through the resistors 94, 62, 60 and 90. The right hand side of capacitor 92 is likewise grounded through the resistors 96 and 98, the switching circuit 42 and the resistors 62, 60 and 90 when the trigger switch 44 is open.

' On closing of the trigger switch 44 the voltage on the lieft side of the capacitor 92 substantially immediately rises to 6.5 volts, causing a positive bias on the transistor 34 due to a positive five-tenths of a volt on the right hand 4 side of the capacitor 92 and consequently con'duct'ion of the transistor 34.

Conducting of the transistor 34 also places the right hand side of the capacitor 84 at approximately five-tenths of a volt positive through the diode 104, whereby the left hand side of the capacitor 84 is causedto go approximately 5.5 volts 'negative to insure that the transistor30 remains turned'ofLThe transistor 30 has been urged toward conductionon closing of the trigger switch 44 due to the application of .the source of energy 12 to the basethereof through the switching circuit 42 and resistors 88. and 86.

Also, conduction ofthe transistor 34 provides a positive bias for the buffer transistor 26'across the resistor to cause conduction of the transistor 26'. When the transistor 26 conducts the six-volt signal from the Zener diode 56 it is applied to the resistors 58 and 70, as shown, to produce closing 'of the switch 16 through transistor 20, as previously indicated.

As the transistor 34 conducts, the negative.5.5 volts now on the left side of the capacitor 84 rises toward the voltage of the source of electrical energy 12 in accordance with the time constant provided by capacitor 84, the resistance 86 and to a lesser extent the variable resistor 88. After a predetermined time the left hand side of the capacitor 84 will go positive to, for example, .5 volt and the transistor 30 will be caused to conduct. On conducting of the transistor 30 a bias is applied across the resistor 106 to the transistor 32 to produce conduction of the transistor 32. Conducting of the transistor 32 will place the left hand side of the capacitor 92 at approximately fivetenths of a volt positive and cause the right hand side of the capacitor 92 to substantially immediately assume a negative 5.5 volts charge.

The transistor 34 is thus cut off when the transistor 30 conducts. Cutting oil of the transistor 34 will cause the right hand side of the capacitor 84 to again assume approximately six volts positive, while the left hand side will return to approximately five-tenths of a volt positive since five-tenths of a volt is dropped across the conducting transistor 30.

The transistor 34 will remain cut off for a period determined by the time constant of the capacitor 92, the variable resistor 96 and the resistor 98. When the charge on the right hand side of the capacitor 92 has again reached'a positive five-tenths of a volt, the transistor 34 will again conduct to cut off the transistor 30 and close the electronic switch 16.

It will thus be seen that the transistor 34 will be energized at the frequency of the'multivibrator circuit 28 to close the electronic switch 16 at the frequency of the multivibrator circuit 28 on closing of the trigger switch 44 with the switching circuit 42 in the second position thereof. Thus, a reduced firing rate of a machinegun connected to be actuated by the solenoid coil 14 of, for example, 200 rounds per minute may be provided.

Referring to the frequency of operation of the multivibrator circuit 28, it will be understood that the transistor 34 is always energized first so that immediately on pressing the trigger switch 44, firing of a machinegun ener gized by the coil 14 will begin.

The operation of the control circuit 10 is stabilized over large changes in supply'voltage by the Zener diode 56. However, the time during which the solenoid 14 is energized or the olf time of the transistor 30 will vary-with the magnitude of the electrical energy from-the source of electrical energy 12. The off time of the transistor'30 may be initially adjusted for a particular value of voltage source by selection of the resistor 88.

With the switching circuit 42 in the third position thereof, the solenoid 14 is'energized with one pulse of electrical energy, whereby a machinegun actuated thereby will fire a single shot. Thus, with the right hand portion of the selector switch 42 in the third position, the multivibrator circuit 28 is converted into a single shot multivibrator.

That is to say, the transistor 34 is maintained in an off condition once the transistor 30 conducts since the right hand side of the capacitor 92 is connected through resistors 96, 98, 108 and 110 to the left hand side of the capacitor 92 which is connected to ground through the conducting transistor 32. With such a connection, the base of the transistor 34 is not permitted to go positive a sufficient amount to turn the transistor 34 on after the initial pulse of energy provided therethrough.

With the switching circuit 42 in the fourth position, again the multivibrator circuit 28 is a single shot multivibrator. However, the single pulse through the transistor 34 and therefore the length of time that the switch 16 is closed is considerably longer since the time constant for discharge of the capacitor 84 now includes the diode 114 and the relatively large resistance of the potentiometer 112.

Also, the voltage supply for potentiometer 112- is reduced by the voltage divider including resistors 60 and 62, and this voltage is more constant because of the stable voltage at the junction of resistor 62 and diode 64 produced by action of Zener diode 56. Thus, the amount of compensation for mechanical delay of actuator is the same as with the switching circuit 42 in the second and third conditions although the percentage of compensation is reduced. The net result is that the single pulse will allow a burst of approximately five rounds from a machinegun controlled by the circuit 10.

The potentiometer 112 allows a field adjustment to permit exactly five rounds to be fired per burst whenever the trigger switch 44 is pressed by varying the time constant of the capacitor 84, resistor 86, and resistance of potentiometer 112, as will be understood by those in the art.

Additionally, it will be seen that in the operation of the multivibrator circuit 28, initially the left hand side of capacitor 92 is at a zero voltage as is the left hand side of capacitor 84. After the first cycle of operation of the mulivibrator, the voltage of the left side of both the capacitors 92 and 84 vary to .5 of a volt. As the result of this dilference in the voltage on the capacitors 84 and 92, th initial energizing of the solenoid coil 14 is for a longer period by approximately ten percent. This dilference in time of operation of the multivibrator circuit 28 compensates for lubricants which may initially be somewhat sticky and for the mechanical rebound found in the operation of many machineguns which will not be initially present.

With the switching circuit 42 in the fifth position, it is desired to put the multivibrator through five cycles of operation thereof and then stop the operation of the multivibrator. Thus, the coil 14 will be energized to provide a slow burst of five single shots from a machine gun actuated thereby on continuous pressing of the trigger switch 44.

To cut off the multivibrator 28 after five cycles of operation thereof, the transistor 38 of the cutoff circuit 36 is caused to conduct after a stepped time delay selected by the value of the capacitor 116, resistor 118, resistor 120 and resistor 122. Turning the transistor 38 on provides a bias on transistor 40 through the resistors 124 and 126 sufficient to turn the transistor 40 on which will again place the base of the transistor 34 at something less than one-half volt above ground through the resistors 96, 98, 108 and 128 and the conducting transistor 40.

Thus, initially the capacitor 116 is at zero volt at the top and six volts on the bottom thereof since transistor 38 is conducting with the switch 44 open. On pressing of the trigger switch 44 a 6.5 volt potential is present on the top of the capacitor -116 and approximately twelve and one-half volts are provided on the bottom of the capacitor 116 to cut the transistor 38 off. During the five subsequent cycles of the multivibrator circuit 28, the capacitor 116 discharges toward a positive six volts at the base of the transistor 38 through a stepped time delay caused by the periodic conduction of transistors 30 and 32 which permits conduction of transistor 38 again after five cycles of operation of the multivibrator circuit 28.

Thus, it will be recognized that there is provided in the control circuit 10 a simple, economical and eificient control for firing a machinegun or the like at ditferent selected rates. Further, it will now be obvious how protection is provided in the control circuit 10 against excessive voltage from the solenoid 14, how the circuit 10 is protected against short circuiting of the solenoid 14, and how lubrication and mechanical rebound compensation and compensation for actuation and release time of the actuator 15 is provided.

I claim:

1. An electronic control circuit for controlling the rate of fire of a machinegun or the like, comprising a source of electrical energy, an actuating transducer, a first electronic switch for energizing the actuating transducer from the source of electrical energy and means for selectively closing the first electronic switch on command to provide continuous energizing of the actuating transducer or a selected pulsed energizing of the transducer, including a second electronic switch connected to the first electronic switch operable on being closed to close the first electronic switch and means including a trigger switch and a third electronic switch in series for closing the second electronic switch on closing of the trigger switch.

2. Structure as set forth in claim 1, wherein the trigger switch is connected to the source of electrical energy and the third electronic switch includes multivibrator means for closing the second electronic switch at a predetermined frequency on closing of the trigger switch.

3. Structure as set forth in claim 2, and further including means operably associated with the multivibrator means for opening the second electronic switch a predetermined time after closing of the trigger switch.

4. Structure as set forth in claim 2, and further including means operably associated with the multivibrator means for selectively rendering .the multivibrator means a single shot multivibrator.

5. Structure as set forth in claim 4, and further including means operably associated with the multivibrator means for varying the length of the single pulse of energy to vary the time during which the second electronic switch is closed.

6. Structure as set forth in claim 1, and further including an energy absorbing circuit connected between the first electronic switch and electromechanical actuating transducer for absorbing energy from the transducer on opening of the first electronic switch.

7. An electronic control circuit for controlling the rate of fire of a machinegun or the like, comprising a source of electrical energy, an actuating transducer, a first electronic switch for energizing the actuating transducer from the source of electrical energy, means for selectively closing the first electronic switch on command to provide continuous energizing of the actuating transducer or a selected pulsed energizing of the actuating transducer and means connected between the first electronic switch and the actuating transducer for preventing continued closing of the first electronic switch on a short circuit occurring at the actuating transducer.

8. An electronic control circuit for controlling the rate of fire of a machinegun or the like, comprising a source of electrical energy, an actuating transducer, a first electronic switch for energizing the actuating transducer from the source of electrical energy, means for selectively closing the first electronic switch on command to provide continuous energizing of the actuating transducer or a selected pulsed energizing of the actuating transducer, and means operably associated with the means 'for closing the first electronic switch for extending the length of the initial pulse of energy through the output transducer by extending the length of time the electronic switch is closed during the first pulse in pulsed energizing of the transducer.

9; Structure as set'forth in claim 8 and further including separate means operably associated with the means for closing the first electronic switch for regulating the length of the pulses through the transducer in accordance with the magnitude of the electric energy supplied from the source of electrical energy to assure substantially constant mechanical operation of the transducer.

- 10. An electronic control circuit for controlling the rate of fire of a machinegun or the like, comprising a source of electrical energy, an actuating transducer, a first electronic switch for energizing the actuating transducer from the source of electrical energy, means for selectively closing the first electronic switch on command to provide continuous energizing of the actuating transducer or a selected pulsed energizing of the actuating transducer and means operably associated with the means for closing the first electronic switch for regulating the-length of the pulses through the transducerin accordance with the magnitude of the electric energy supplied from the source of electrical energy to assure substantially constant mechanical operation of the transducer.

References Cited UNITED STATES PATENTS 2,331,402 4/1958 Taslitt 89-129 X 3,1 4 2,0 25 7/1964 Roberts 30-7'276 X SAMUEL FEINBERG, Primary Examiner. STEPHEN C. BENTLEY, Assistant Examiner.

US. Cl. X.R. 307-132,'247, 276 

